Prevalence of polymorphism (“crossover”) among sexual offenders

Abstract Polymorphic or crossover sexual offenders have victims in different categories (e.g., adult and child victims; male and female victims; related and non-related victims). The present study systematically reviewed and synthesized the existing literature in an effort to ascertain the prevalence of crossover among sexual offenders that takes into account potentially relevant methodological features that might affect the estimates. Our search yielded 47 studies involving 35,572 contact sexual offenders. Key findings include: The mean prevalence of offenders who had both adult and child victims was 19.1% (based on 43 studies); the mean prevalence of offenders who had both male and female victims was 15.2% (based on 20 studies); the prevalence of offenders who had both related and non-related victims was 19.9% (based on 21 studies). Prevalence estimates more than doubled when the outcome measure is unofficially detected offending (ascertained via self-report or polygraph) versus officially detected offending (e.g., criminal justice statistics). The prevalence of victim age crossover was higher when the sample preselected offenders with multiple known victims, though sample preselection did not affect the prevalence of victim gender or relationship crossover. The nation in which the study was conducted does not appear to influence the prevalence of crossover offending.